1. Technical Field
The present disclosure relates to advances in medical systems and procedures for prolonging and improving human life and, more particularly, to novel electrosurgical instruments for tissue ablation, systems for tissue ablation including the electrosurgical instruments, and methods for ablating tissues containing abnormalities such as cancerous tumors using the systems for tissue ablation.
2. Discussion of Related Art
Therapeutic lesions in living bodies have been accomplished for many decades using radio-frequency (RF) and other forms of energy. The procedures have been particularly useful in the field of neurosurgery, typically where RF-ablation electrodes (usually of elongated cylindrical geometry) are inserted into a living body. A typical form of such ablation electrodes incorporates an insulated sheath from which an exposed (uninsulated) tip extends.
Generally, the ablation electrode is coupled between a grounded RF power source, e.g., an electrosurgical generator, (outside the body) and a reference ground or indifferent electrode, e.g., return electrode, for contacting a large surface of the body. When an RF voltage is provided between the ablation electrode and the reference ground, RF current flows from the ablation electrode through the body. Typically, the current density is very high near the tip of the ablation electrode, which heats and destroys the adjacent tissue.
In the past, RF ablation electrodes have incorporated temperature sensors, for example, in the form of a thermistor or thermocouple as disclosed in U.S. Pat. No. 4,411,266 to Cosman. Typically, the sensor is connected to a monitoring apparatus for indicating temperature to assist in accomplishing a desired lesion. As generally known, for a given tip geometry and tip temperature, lesions of a prescribed size can be made quite consistently, also disclosed in U.S. Pat. No. 4,411,266 to Cosman.
Over the years, a wide variety of RF electrode shapes and configurations have been used, for example, several current forms are available from Radionics, Inc., located in Burlington, Mass. Such electrodes have been used to accomplish lesions in a wide variety of targets within the body, including the brain, the spinal column and the heart.
An important criterion when using electrode ablation systems relates to the temperature of the tip achieved during the ablation process. Specifically, it is desirable to maintain the temperature of certain ablation electrodes, of a given tip geometry, below 100° C. At a temperature at or above 100° C., the tissue surrounding the ablation electrode will tend to boil and char. Consequently, the lesion size for a given electrode geometry generally has been considered to be somewhat limited by the fact that the tissue near the tip must not exceed 100° C.
Essentially, during RF ablation, the electrode temperature is highest near the tip, because the current density is the highest at that location. Accordingly, temperature falls off as a function of distance from the electrode tip and, except for possible abnormalities in tissue conductivity and so on, in a somewhat predictable and even calculable pattern. As an attendant consequence, the size of RF lesions for a given electrode geometry have been somewhat limited.
One proposed solution to the limitation of lesion's size has been to employ “off-axis” electrodes, for example the so called Zervas Hypophysectomy Electrode or the Gildenberg Side-Outlet electrode, as manufactured by Radionics, Inc., Burlington, Mass. However, such systems, in requiring multiple tissue punctures, increase trauma to the patient.
Considering lesion size, it has been seen that lesions in the brain of up to 10 to 12 millimeters, by using very large ablation electrodes, may be produced. However, in order to produce similarly sized lesions or larger sized lesions with relatively smaller ablation electrodes, ablations systems including ablation electrodes with conduits which deliver cooling fluid to the tip thereof have been developed. Reference may be made to U.S. Pat. Nos. 5,951,546; 6,506,189; 6,530,922; and 6,575,969, the entire contents of each of which being incorporated herein by reference, for a detailed discussion of such systems. Generally, ablation electrodes with cooled conductive tips produce larger lesion volumes as compared to ablation tips which are not cooled.
Accordingly, a need exists for electrosurgical instruments for tissue ablation, systems for tissue ablation including the electrosurgical instruments, and method for ablating tissues containing abnormalities such as cancerous tumors using the systems for tissue ablation.